The present invention relates to a method for the transmission of data among mobile or autonomous vehicles having no absolute time reference and communicating with one another by radio link on a single channel with a limited range such that the propagation time remains negligible as compared with the reaction time t.sub.r of the receivers.
With a method such as this, if it is assumed that a vehicle is within effective range when the signal-to-noise ratio at reception remains at an appropriate level, then the only risk that a message will not be received arises out of the fact that it collides with another message transmitted at the same instant in a same perimeter by another vehicle.
The collisions take place notably when two vehicles B and C, within range of one and the same third vehicle A, transmit simultaneously towards this vehicle. There are then two possibilities depending on whether or not the two transmitting vehicles B and C are linked (i.e. are within radioelectrical range of each other) or are not linked and are concealed from each other by a third vehicle interposed between them.
In the former case, procedures known as CSMA or Carrier Sense Multiple Access procedures (i.e. listening for the freedom of the channel before transmission) enable the collisions to be greatly reduced.
However, in the latter case, there is no access procedure by which these collisions can be prevented, and this is detrimental to many applications such as, for example, those relating to road safety in inter-city or urban areas when it is imperative to make accurate transmission of at least one message during determined periods of time that are relatively short (for example 100 ms) to other mobile bodies or vehicles within effective range.